With the global total of emissions likely to come in at around 52 gigatonnes this year, we're already at the edge, according to new research

UXBRIDGE, Canada, Dec 17 2012 (IPS) - The most important number in history is now the annual measure of carbon emissions. That number reveals humanity's steady billion-tonne by billion-tonne march to the edge of the carbon cliff, beyond which scientists warn lies a fateful fall to catastrophic climate change.

With the global total of climate-disrupting emissions likely to come in at around 52 gigatonnes (billion metric tonnes) this year, we're already at the edge, according to new research.

To have a good chance of staying below two degrees C of warming, global emissions should be between 41 and 47 gigatonnes (Gt) by 2020, said Joeri Rogelj, a climate scientist at Switzerland's Institute for Atmospheric and Climate Science in Zurich.

"Only when we see the annual global emissions total decline will we know we're making the shift to climate protection," Rogelj told IPS.Making the shift to a future climate with less than 2C of warming is doable and not that expensive if total emissions peak in the next few years and fall into the 41-47 Gt "sweet spot" by 2020, Rogelj and colleagues show in their detailed analysis published Sunday in the journal Nature Climate Change.

The study is the first to comprehensively quantify the costs and risks of emissions surpassing critical thresholds by 2020.